The present invention relates to a novel arrangement for transporting solid bulk materials and a vessel for storing and discharging such materials.
Prior to the present invention it was known to employ fluidizing gravity conveyors for transporting solid particulate material. Fluidizing gravity conveyors are generally illustrated in U.S. Pat. No. 2,527,455. Such apparatus includes a channel member having gas impervious bottom, side walls and end walls. A gas permeable material such as fabric closes the top of the channel. A closed material chamber may be provided above the fabric.
The apparatus is mounted at an incline. Air under pressure is supplied to the plenum chamber defined by the channel for passage through the gas permeable fabric to aerate the material in the material chamber. This causes the solid particulate material to act as a liquid. Solid particulate material to be conveyed moves down the inclined apparatus, along the gas permeable material through the upper channel by means of gravity.
Fluidizing gravity conveyors are well suited to conveying certain types of finely divided material, but are not well suited to other solid bulk material. As referred to in the present application, solid bulk material is intended to include finely divided solid material such as cement clinker and alumina which are normally considered as readily fluidizable and less finely divided materials such as stone, beans and the like which are not easily fluidizable, particularly when considering the air velocities normally associated with a fluidizing gravity conveyor. Fluidized gravity conveyors have not been well suited to transporting large particles of material such as stones and beans. A further disadvantage with fluidized gravity conveyors is that with certain materials the angle at which the conveyor must be set in order to convey material is often larger than one might desire. This is particularly true when head room in a plant location is minimal.
In storage vessels for bulk materials, fluidizing gravity conveyors without closed material chambers above the gas permeable fabric are used for aerating material in the vessel in order to permit the material to flow freely toward the outlet of the vessel. Conventionally, these conveyors are sloped from the end of the vessel toward a sump and the vessel outlet is located at the sump.
Also known prior to the present invention was the use of a pneumatic diverting valve for the purpose of pulsing the air supplied to a fluidizing gravity conveyor to assist in the conveying of materials. A prior U.S. Patent showing such an arrangement is U.S. Pat. No. 3,469,888 issued Sept. 30, 1969. The inventor of the present application is a co-inventor of that patent. In that patent, a railway car or other vessel is divided into a material chamber and a plenum chamber by a sloping, air permeable, flexible fabric divider with the fabric being at a substantial slope toward the vessel outlet. There are two plenum chambers and an oscillating valve operating at a frequency of about 2 to 20 cycles per minute and a preferred frequency of 5 to 6 cycles per minute alternates air flow between the two plenum chambers. The intended purpose of the cycling is to produce high velocity shock waves which serve to break up compacted material above one of the plenum chambers. Once the compacted material is broken up, the air which is steadily supplied to one of the plenum chambers between cycles will fluidize material above that plenum chamber for a certain period of time, say 12 seconds if a frequency of 5 cycles per minute is used. So long as air is supplied to the plenum chamber, the material is fluidized. Once the material is fluidized, it will flow down the sloped fabric to the material outlet in a manner well known in fluidizing gravity conveyors. The oscillating valve of the above prior patent will then rapidly switch the air supply to the other plenum chamber producing a shock wave to break up compacted material and continue the air supply to that plenum chamber for the selected time period so that material above that plenum chamber is fluidized and conveyed to the vessel outlet. Since there is a substantial time span during which no air is supplied to the first plenum chamber, material above that first plenum chamber will become deaerated and stop flowing. As a result, there is not total increase in the capacity of material discharged from the vessel but only an improved ability to remove material from the vessel. The apparatus is primarily of value for discharging difficult to fluidize material from a vessel. As is apparent from U.S. Pat. No. 3,469,888, the need for complex "slope sheets" and "crickets" within the material chamber to increase material flow has not been eliminated by the patent.
Sloping the conveyors within a vessel for pulverulent material has the significant disadvantage that a substantial portion of the vessel must be taken up by the sloped conveyors, and the accompanying slope sheets and crickets. The greater the slope of the conveyors, the less space available in the vessel. In addition, this complex arrangement substantially increases the manufacturing cost of the vessel. Even with the large slope angle of the conveyors or aeration units and the use of slope sheets and crickets, these vessels are not usable for all bulk materials. Prior to the present invention it was known to combine a fluidizing gravity conveyor with means for vibrating the gas permeable member dividing the plenum chamber and the material chamber. A prior system for doing this is shown in British Specification No. 712,593 published July 28, 1954 which shows an electro magnetic arrangement for vibrating the gas permeable member. A similar arrangement is shown in U.S. Pat. No. 3,519,310 except that a Sonic generator (horn) is used instead of a vibrator directly attached to the fabric. These arrangements have the disadvantage of requiring some means in addition to the steady fluidizing air to achieve the desired vibration. A sonic generator can create a noise problem of a type not normally associated with the type of equipment referred to by the present invention and usually undesirable. The use of an electro magnetic vibrator necessitates the use of electric wiring in a dusty application which is usually undesirable.
Other apparatus for pulsing air supplied to the plenum chamber of a fluidizing gravity conveyor type apparatus were also known prior to the present invention. One such apparatus is shown in U.S. Pat. No. 2,844,361 which relates to a blending apparatus and uses pulses of supplemental air to break up open areas in the material. In that patent, a mechanical means is used for pulsing which inherently limits the frequency of pulsing obtainable. It is not believed that sufficiently rapid pulsing of the air can be achieved to increase conveying capacity. In addition, the material is continuously aerated by one source of air and pulsed by air supplied by a second source. The fact that there are two sources of air insure that the material will not become deaerated between pulses but obviously does not reduce the use of compressed air.
The use of lobed rotor blowers as a means for supplying air to fluidizing gravity conveyors is a common practice. These blowers inherently rapidly pulse the air supplied to the plenum chamber. The pulses will occur at the rate of four times the speed of the blower which may result in a total of 1,000 pulses per minute and more. This pulsing is not an on-off type of pulse. There is no noticeable difference in conveying capacity between steady state air supply and air supplied by a lobed rotor blower.
Thus, prior apparatus which pulsed air supplied to the plenum chamber of a fluidizing gravity conveyor or vibrated the fabric usually required additional apparatus to achieve the vibration or pulsing and even where additional apparatus was not required, increased capacity was not achieved.